doc: Update more docstrings to have one sentence summary as first line. Reviewed specfun, special-matrix, testfun, and time script directories. * scripts/specfun/expint.m, scripts/specfun/isprime.m, scripts/specfun/legendre.m, scripts/specfun/primes.m, scripts/specfun/reallog.m, scripts/specfun/realsqrt.m, scripts/special-matrix/gallery.m, scripts/special-matrix/hadamard.m, scripts/special-matrix/hankel.m, scripts/special-matrix/hilb.m, scripts/special-matrix/invhilb.m, scripts/special-matrix/magic.m, scripts/special-matrix/pascal.m, scripts/special-matrix/rosser.m, scripts/special-matrix/toeplitz.m, scripts/special-matrix/vander.m, scripts/special-matrix/wilkinson.m, scripts/testfun/assert.m, scripts/testfun/demo.m, scripts/testfun/example.m, scripts/testfun/fail.m, scripts/testfun/rundemos.m, scripts/testfun/runtests.m, scripts/testfun/speed.m, scripts/time/asctime.m, scripts/time/calendar.m, scripts/time/clock.m, scripts/time/ctime.m, scripts/time/datenum.m, scripts/time/datestr.m, scripts/time/datevec.m, scripts/time/etime.m, scripts/time/is_leap_year.m, scripts/time/now.m, scripts/time/weekday.m: Update more docstrings to have one sentence summary as first line.

syntax: regexp
# The recurrent (^|/) idiom in the regexps below should be understood
# to mean "at any directory" while the ^ idiom means "from the
# project's top-level directory".

# gnulib makes these silly backup files
.~$

# This directory gets created by gnulib during the build. 
# It contains no Octave files.
^libgnu/*

# This directory mostly contains cruft during build time, but it does
# contain some Octave code, so we gotta be a bit more careful about
# what we ignore here
^m4/(?!ax_).+\.m4$

# Emacs tools create these
(^|/)TAGS$
(^|/)semantic.cache$

(/|^)Makefile\.in$
^INSTALL$

^aclocal\.m4$
^build-.*($|/)
^configure$
^autom4te\.cache($|/)
^config\.in\.h$

# e.g. doc/faq/OctaveFAQ.info
#      doc/interpreter/octave.info-4
^doc/.*\.info(-\d)?$

^doc/\w*/stamp-vti$
^doc/\w*/version\.texi$
^doc/interpreter/images\.mk$

# e.g. liboctave/operators/smx-op-inc.mk
^liboctave/operators/\w+-op-\w+\.mk$

^libinterp/dldfcn/module\.mk$